Ignition timing control system for internal combustion engines

ABSTRACT

In ignition timing control system for an internal combustion engine, a knocking detector is provided to detect knockings of the engine, and a control unit responsive to the knocking signals of the knocking detector to provide a variable retard amount signal per one knocking which depends on whether the occurrence of another knocking is decided before the lapse of a predetermined time interval from the decision of the knocking.

BACKGROUND OF THE INVENTION

The present invention relates to an ignition timing control systemhaving the functions of detecting a knocking by a vibration or a noisegenerated in or outside of a cylinder of an internal combustion engineby the pressure therein and retarding the ignition timing if a knockingis detected.

In recent years, what is called the knocking feedback system fordetecting a knocking caused in an internal combustion engine andretarding the ignition timing has been studied variously. Such a systemwill be described briefly. Specifically, a vibration or a noise causedin or outside of an internal combustion engine is detected by thepressure in the cylinder, and if the vibration or the noise, as the casemay be, exceeds a set level (a knocking decision level), a knocking isdecided thereby to generate a knocking signal. When this knocking signalis generated, the ignition timing is retarded, while in the absence of aknocking signal, the ignition timing is advanced, so that the ignitiontiming is always controlled to a knocking limit or thereabouts therebyto improve the fuel efficiency and output performance of the engine.

In this knocking feedback system, the amount of retard per knocking upondetection of a knocking is predetermined and generally approximately 1°CA (crank angle). This retard amount per knocking is a most importantfactor affecting the controllability of the ignition timing. This willbe explained with reference to FIG. 1. As seen from FIG. 1, in order toimprove both the ignition timing controllability under normal conditionsand the ignition timing response under transient conditions, it isabsolutely necessary to discriminate the normal and transient conditionsand switch the retard amount per knocking therebeween.

Conventionally, however, for lack of means for discriminating the normaland transient conditions accurately, it has so far been impossible toswitch the retard angle per knocking. In the method of switching theretard amount by detecting the acceleration of the engine, for instance,an unnecessarily large retard may be caused by a setting of a largeretard, often deteriorating the engine acceleration performance, due tothe fact that the difference of engines or environmental conditions maylead to a small knocking even under an accelerated state. For thisreason, the retard amount is conventionally set at a compromise (such as1° CA) between the normal and transient conditions, with the result thatthe performance is deteriorated unavoidably under both normal andtransient conditions.

SUMMARY OF THE INVENTION

In view of the above problem, a first object of the present invention isto provide an ignition timing control system for internal combustionengines wherein in the case where knocking signals is produced from aknocking detector circuit successively for a comparatively short periodof time predetermined according to the engine conditions including theengine speed, a transient condition is immediately decided so that theretard amount per knocking is increased for an improved transientoperating performance, while in the case where knocking signals fail tobe produced successively for the same period of time, a normal conditionis decided so that the retard amount per knocking is held at acomparatively small level for an improved normal operating performance.

This process is based on the fact that under normal conditions knockingsoccur comparatively infrequently with the ignition timing controlled bya knocking feedback system, thereby leading to a comparatively longintervals of knockings, whereas under transient conditions such assudden acceleration, knockings occur at intervals of about 1 to 3cycles, resulting in short intervals of knockings, and on the fact thatthe intervals of knockings under normal conditions depend on the engineconditions such as engine speed or engine vacuum and therefor it isimpossible to accurately discriminate the normal and transientconditions unless the period for which knockings are detected is changedaccording to the engine conditions.

Further, under an idling condition involving a very low speed, emphasisis placed on the starting output disregarding the knocking sound to somedegree under transient conditions and for this reason the retard amountis rather required to be held at a low level. In a high speed range ofabout 4000 rpm or more, on the other hand, mechanical noises are appliedto the knocking detector so that an erroneous knocking decision maycause knocking pulses to be produced successively for a very shortperiod of time. Under these special engine conditions, it is desirableto substantially nullify the function of changing the retard amount inaccordance with the successive occurrence of knockings. A second objectof the invention is attained by such a feature.

According to the present invention, the normal and transient conditionsare discriminated always accurately for all engine conditions by thesignals produced from a knocking detector, thus greatly improving theperformance under both normal and transient conditions as compared withthe prior art. Also, a transient condition detector is not providedseparately, thus improving the performance at low cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a characteristic diagram showing the relation between thechange of ignition timing and retard amount.

FIG. 2 is a diagram showing a general configuration of a firstembodiment of the present invention.

FIG. 3 is a diagram showing a detailed configuration of a knockingdetector circuit in FIG. 2.

FIG. 4 shows signal waveforms produced at various parts in FIG. 3.

FIG. 5 is a diagram showing a detailed configuration of the retardamount changing circuit and the retard amount computing circuit in FIG.2.

FIG. 6 shows signal waveforms produced at various parts in FIG. 5.

FIG. 7 is a diagram showing a detailed configuration of the retardamount changing circuit and the retard amount computing circuit in asecond embodiment of the present invention.

FIG. 8 shows signal waveforms produced from various parts in FIG. 7.

FIG. 9 is a diagram showing a detailed configuration of the retardamount changing circuit in a third embodiment of the present invention.

FIG. 10 is a diagram showing a general configuration of a fourthembodiment of the present invention.

FIG. 11 is a diagram showing a detailed configuration of the ignitiontiming control circuit in FIG. 10.

FIG. 12 is a flowchart showing the sequence of operating processes inthe ignition timing control circuit shown in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1(a) and 1(b) represent variations of ignition timing under normalconditions, and FIG. 1(c) shows the response of ignition timing undertransient conditions. In FIGS. 1(a) to 1(c), the abscissa representstime, and the ordinate ignition timing.

Variations of ignition timing under normal conditions involving a largeretard amount per knocking (such as 2° CA) are shown in FIG. 1(a), andvariations of ignition timing under normal conditions involving a smallretard amount per knocking (such as 0.5° CA) are shown in FIG. 1(b). InFIGS. 1(a) and 1(b), the one-dot chain represents the ignition timingproviding a target for ignition timing control, which is generally theignition timing of trace knock limit. At this ignition timing, theengine is properly knocked for an improved fuel consumption rate andoutput. Comparison between FIGS. 1(a) and 1(b) shows that thecontrollability under normal conditions increases with the decrease ofthe retard amount per knocking (FIG. 1(b). This is explained by the factthat when a large retard amount is involved (FIG. 1(a), the ignitiontiming is displaced greatly from the target ignition timing, so that ifthe ignition timing is displaced toward the advanced side, the knockingsound increases, while if the ignition timing is displaced toward theretarded side, the loss of output and fuel consumption are caused.

If the retard amount per knocking is reduced excessively, however, thesound-deadening effect on the knocking is reduced. The retard amount ofabout 0.3 to 0.5° CA is therefore preferable under normal conditions. Asseen from above, the controllability of ignition timing under normalconditions is improved with the decrease in the retard amount perknocking.

The reverse is the case for the ignition timing response under transientconditions. The ignition timing response under transient conditions(sudden acceleration) is shown in FIG. 1(c). In FIG. 1(c), referencenumeral 1 designates the response for a small retard amount (say, 0.5°CA), and numeral 2 the response for a large retard amount (say, 2° CA).This graph shows that in the case where the retard amount per knockingis small (such as 1), the ignition timing response is low so that undertransient conditions such as sudden acceleration, knockings occursuccessively to the discomfort of the driver, finally damaging theengine. Under transient conditions, therefore, the retard amount perknocking is required to be increased.

The present invention will be explained below with reference to anembodiment shown in FIG. 2 to 12. FIG. 2 is a block diagram showing afirst embodiment of the present invention. In FIG. 2, reference numeral1 designates a knocking detector for detecting variations of the engineassociated with the knocking thereof by a piezoelectric element orelectromagnetic means such as magnet or coil. Numeral 2 designates asignal generator which is incorporated in a distributor (not shown) forsetting a basic ignition timing in accordance with a vacuum advancedevice. Numeral 3 designates a control unit for determining an actualignition timing in response to signals from the knocking detector 1 andthe signal generator 2 and producing an ignition timing control signal,and numeral 4 an ignitor for current-amplifying the ignition timingcontrol signal for deenergizing the ignition coil (not shown). Theignition timing control circuit 3 is configured as described below.Numeral 31 designates a knocking detector circuit for detecting whetheror not a knocking of the engine has occurred in response to an output ofthe knocking detector 1, numeral 32 a waveform shaping circuit forwaveform-shaping the pickup signal of the signal generator 2 andproducing a basic ignition timing, and numeral 33 a retard amountchanging circuit for detecting whether or not knockings of the enginehave occurred successively within a predetermined length of timedepending on the engine conditions (the engine speed in this embodiment)in response to the knocking signal produced from the knocking detectorcircuit 31 and changing the retard amount per knocking in accordancewith the occurrence of the knockings. Numeral 34 designates a retardamount computing circuit for computing the retard amount behind thebasic ignition timing in response to the knocking signal produced fromthe knocking detector circuit 31 and the retard amount signal associatedwith the retard amount per knocking produced from the retard amountchanging circuit 33, and numeral 35 an ignition timing computing circuitfor determining an actual ignition timing by subtracting the retardamount produced from the retard amount computing circuit 34 from thebasic ignition timing produced from the waveform-shaping circuit 32.

Now, the configuration of the knocking detector circuit 31 will bedescribed in detail with reference to FIG. 3. Numeral 311 designates afilter such a bandpass or high-pass filter for picking up knockingfrequency components selectively out of the output of the knockingdetector 1, numeral 312 a half-wave rectifier for half-wave-rectifyingthe output of the filter 311, numeral 313 an integrator for integratingthe output of the halfwave rectifier 312 and producing the average valueof the vibration output of the knocking detector 1, numeral 314 anamplifier for amplifying the output of the integrator 313 and producingan appropriate knocking decision level, numeral 315 an offset voltagesetter including a resistor for shifting a voltage in order to producean effect of noise margin or the like in the output of the amplifier314, numeral 316 an adder for adding the output of the amplifier 314 tothe output of the offset voltage setter 315 and producing a finalknocking decision level, numeral 137 a comparator for comparing theoutput of the half-wave rectifier 312 with that of the adder 316 and,when the output of the half-wave rectifier 312 is larger, deciding thata knocking has occurred and producing an output voltage, and numeral 318a monostable multivibrator triggered at the leading edge of the outputof the comparator 317 to hold the voltage signal involved for apredetermined length of time from the triggering.

The operation of this knocking detector circuit will be explained withreference to FIG. 4. FIG. 4(a) shows an output signal of the filter 311,that is, a signal obtained by selectively picking up the knockingfrequency component (6 to 9 KHz) out of the output of the knockingdetector 1. In FIG. 4(a), characters a_(l), a₂ and a₃ designate outputscorresponding to three different knockings. Specifically, a_(l)represents a comparatively small knocking, a₂ a comparatively largeknocking, and a₃ a noise or a very small knocking. FIG. 4(b) shows asignal obtained by half-wave rectifying the signal of FIG. 4(a) by therectifier 312, and FIG. 4(c) a signal obtained by integrating andamplifying the signal of FIG. 4(b) by the integrator 313 and theamplifier 314. FIG. 4(d) shows a signal obtained by adding the offsetvoltage to the signal of FIG. 4(c) by the adder 316 (that is, a knockingdecision level), which is plotted together with the output signal of therectifier 312 (FIG. 4(b) by way of comparison. FIG. 4(e) shows an outputsignal of the comparator 317, which is raised to high state when theoutput signal (FIG. 4(b) of the rectifier 312 is larger than theknocking decision level (FIG. 4(d) and is reduced to low state in theopposite case. FIG. 4(f) shows an output signal of the monostablemultivibrator 318 which is triggered at the leading edge of the outputsignal of FIG. 4(e) of the comparator 317 and held at high level for apredetermined length T_(l) of time. As a result, when a knocking occurs,a knocking pulse is produced once for each combustion cycle regardlessof the magnitude of the knocking.

Now, the configuration and operation of the retard amount changingcircuit 33 and the retard amount computing circuit 34 making up theessential parts of the present invention will be explained in detail.

FIG. 5 shows a detailed configuration of the retard amount changingcircuit 33 and the retard amount computing circuit 34. In FIG. 5,numeral 3301 designates a monostable multivibrator triggered at the fallof the monostable multivibrator 318 and held at high state for apredetermined length of time T₂, numeral 3302 a switch including atransistor or the like which is turned on to conduct only when themonostable multivibrator 3301 is at high level, numeral 3303 a constantcurrent source for supplying a constant current I_(l), numeral 3305 acharge-discharge capacitor, and 3306 a well-known frequency-voltageconverter (hereinafter referred to as the F/V converter) for convertinginto a voltage the frequency of the signal obtained by waveform-shapingthe pickup signal of the signal generator 2 through the waveform-shapingcircuit 32. Numeral 3307 designates a comparator for comparing thevoltage level of the capacitor 3305 with the voltage level of the F/Vconverter and producing a high level signal when the voltage level ofthe capacitor 3305 is higher. Numerals 3309 and 3310 designate constantcurrent sources for supplying constant currents I₃ and I₄, numeral 3308a switch for switching the constant current sources 3309 and 3310 inaccordance with high or low state of the output of the comparator 3307,numeral 341 a switch which is turned on only when the monostablemultivibrator 318 produces a knocking pulse, numeral 342 a constantcurrent source for discharging a constant current I₅, numeral 343 achange-discharge capacitor, and numeral 344 a buffer for taking out thevoltage of the capacitor 343 in stable manner.

The operation of the retard amount changing circuit 33 and the retardamount computing circuit 34 with reference to FIG. 6, in which theabscissa represents the time and the ordinate the voltage. FIG. 6(a)represents knocking pulses produced from the monostable multivibrator318. FIG. 6(b) shows an output of the monostable multivibrator 3310which is triggered at the leading edge of the knocking pulse and held athigh level for a predetermined length of time T₂. When the output signal(FIG. 6(b) of the monostable multivibrator 3301 is raised to high state,the switch 3302 is turned on so that the constant current I₁ is suppliedto the charge-discharge circuit 3304 and 3305, with the result that thecapacitor 3305 charges and discharges as shown in FIG. 6(c). FIG. 6 (d)shows the waveform of the pickup signal produced from the signalgenerator 2. In FIG. 6(d), one dot chain represents a threshold levelfor shaping the waveform of the pickup signal by the waveform shapingcircuit 32. FIG. 6 (e) shows a signal obtained by waveform-shaping thepickup signal by the waveform-shaping circuit 32. The pickup signal ofthe signal generator 2 is generated in synchronism with the enginespeed, and therefore, when the engine speed changes from low to high,for instance, the pickup signal is "compressed" along the time axis (thefrequency increases) as shown in FIG. 6(d). As a result, the duty factorof the waveform-shaped signal (FIG. 6(e) changes with the increase inthe frequency in accordance with the engine speed. This signal isfrequency-voltage converted at the F/V converter thereby to produce asignal as shown in FIG. 6 (f). The F/V converter is of two types, onefor increasing the voltage with the increase of frequency, the other fordecreasing the voltage with the increase of frequency. This embodimentuses an F/V converter of the latter type in which the voltage isdecreased with the increase of frequency. Thus, as shown in FIG. 6(f),the voltage changes downward when the frequency of the pickup signal ofthe signal generator increases with the increase of engine speed.

The voltage level (FIG. 6(c)) of the capacitor 3305 is compared with thethreshold level (FIG. 6(f)) set by the F/V converter at the comparator3307 as shown in FIG. 6(g). In FIG. 6 (g), the solid line represents thevoltage level (equal to FIG. 6 (d)) of the capacitor 3305, and theone-dot chain represents the threshold hold level (equal to FIG. 6(f)).The graph of FIG. 6(h) shows the output of the comparator 3307. Thissignal is held high only when the voltage level of the capacitor 3305 ishigher than the threshold level. The time Tc during which the signalunder consideration is held at high level is capable of being set asdesired by the current value of the constant current source 3303 and thecapacitance of the capacitor 3305. Once the constants thereof aredetermined, however, the time Tc changes with the change of thethreshold level. The time Tc thus changes with the engine speed. In thisway, the signal of FIG. 6(h) functions as a timer for counting thepredetermined time Tc determined by the engine speed from the occurrenceof a knocking. FIG. 6(h) shows the manner in which with the increase ofengine speed, the threshold level is decreased and the time Tc isincreased accordingly. In the event that another knocking occurs beforehaving counted the predetermined time Tc, the time counting is of courseresumed at that particular point. Depending on whether the output signal(FIG. 6(h)) of the comparator 3307 is high or low, the switch 3308 isoperated, so that the constant current source 3309 or 3310 is turned on.On the assumption that the constant current I₃ is larger than I₄, theconstant current source 3309 is turned on when the signal of FIG. 6(h)is at high level, while the constant current source 3310 is turned onwhen the signal of FIG. 6(h) is at low level, so that a larger currentI₃ is supplied when the signal is at high level.

The knocking pulse (FIG. 6(a)) produced from monostable multivibrator318 activates the switch 341 of the retard amount computing circuit 34.When the switch 341 is turned on, the current I₃ or I₄ determined by theretard amount changing circuit 33 is supplied to the charge-dischargecircuits 342 and 343. The voltage of the capacitor 343 under thiscondition provides an actual retard amount. The voltage of FIG. 6(i)corresponds to such a retard amount. When the interval of two knockingsis shorter than the time Tc set according to the engine speed, it isdecided that a transient condition is involved so that the retard amountper knocking is increased; while the interval of two knockings is longerthan the time Tc, on the other hand, it is decided that the normalcondition is involved and a small retard amount is maintained. Byadjustment of the zero point of the threshold level or gain, thethreshold level is increased in very low speed range thereby toextremely shorten the time T, thus substantially mullifying the functionof increasing the retard amount.

A second embodiment of the present invention is shown in FIG. 7. Thisembodiment is different from the first embodiment in that the thresholdlevel applied to the comparator 3307 is fixed and the discharge of thecharge-discharge circuits 3304 and 3305 in FIG. 5 is changed with enginespeed. The configuration of this embodiment will be described withreference to FIG. 7. Numeral 3317 designates an F/V converter which isdifferent from that of the first embodiment in that the voltage thereofincreases with the increase of frequency. Numeral 3316 designates athreshold voltage setter including a resistor or the like, and numeral3315 a comparator for comparing the output of the F/V converter 3317with the threshold level and producing a high-level signal when theoutput of the F/V converter is larger. Numerals 3312 and 3313 designateconstant current sources for supplying constant currents I₆ and I₇respectively, numeral 3314 a switch for turning on the constant currentsource 3312 or 3313 in accordance with the output level of thecomparator 3315, and numeral 3311 a threshold voltage setter for settinga threshold level.

The operation of this circuit will be explained with reference to FIG.8. FIG. 8(a) shows knocking pulse signals, FIG. 8(b) an output of themonostable multivibrator 3301, FIG. 8(c) a pickup signal produced fromthe signal generator, and FIG. 8(d) a signal obtained bywaveform-shaping the pickup signal. The operation of these circuits weredescribed in the first embodiment and will not be explained again. FIG.8(e) shows an output voltage of the F/V converter 3317 which increaseswith engine speed (the principle being the same as that of the firstembodiment). The one-dot chain in FIG. 8(e) shows a voltage producedfrom the threshold voltage setter 3316. FIG. 8(f) shows an output of thecomparator 3315. Depending on whether the output signal (FIG. 8(f) ofthe comparator 3315 is high or low, the switch 3314 is changed over toturn on the constant current source 3312 or 3313. Assuming that theconstant current I₆ is smaller than I₇, the constant current source 3312is turned on when the signal of FIG. 8(f) is at high level, and theconstant current source 3313 is turned on when the signal of FIG. 8(f)is at low level, so that the smaller current I₆ is supplied when thesignal is at high level. The engine speed N_(l) determined by thethreshold level voltage setter 3316 is thus set as a boundary, and thecomparatively small constant current I₆ is supplied at engine speedshigher than N_(l), while the comparatively large constant current I₇ issupplied at engine speeds lower than N_(l), thus switching thedischarging condition of the capacitor 3305. FIG. 8(g) shows suchcharge-discharge conditions of the capacitor 3305. The one-dot chain inFIG. 8(g) represents the threshold level of the threshold voltage setter3311. FIG. 8(h) shows the output of the comparator 3307, from which itis seen that the time Tc ischanged in accordance with the engine speed.The operation of subsequent stages will not be explained as they areidenticaql to those of the first embodiment. By regulating the values ofcurrents I₆ and I₇ and reducing the time Tc sufficiently in the enginespeed ranges above or below the engine speed N₁, it is of coursepossible to substantially nullify the function of changing the retardamount in the respective ranges.

Instead of deciding the interval of knockings by time as in the firstand second embodiments, it may alternatively be decided by the number ofignition cycle as shown in FIG. 9 as a third embodiment. The operationof the third embodiment shown in FIG. 9 will be explained. The pickupsignal produced from the signal generator 2 is shaped in waveform by thewaveform-shaping circuit 32 and applied as a clock signal to thecounters 3318 and 3319. The pickup signal is a basic ignition timingsignal produced in advance of the combustion cycle of each cylinder todetermine the basic ignition timing of each cylinder. By counting theoutput signal obtained by shaping the waveform of the basic ignitiontiming signal, therefore, it is possible to determine the number ofcycles. The counters 3318 and 3319 are reset by the signal produced fromthe monostable multivibrator 3301, so that the counters 3318 and 3319begin to count the number of ignition cycles in response to theoccurrence of a knocking. If different constants (assumed to be C_(l)and C₂) are set in the counters 3318 and 3319 in advance, the counter3318 counts the number of ignition cycles in response to the occurrenceof a knocking, thereby produce an output signal when the number ofcycles has reached C₁, while the counter 3319 produces an output signalwhen the number of cycles has reached C₂. The output signals are appliedthrough a switch 3321 as a reset signal for a reset-set (R-S) flip-flop,and the switch 3321 activates the counter 3318 or 3319 by the functionsof the F/V converter 3317, the threshold voltage setter 3316 and thecomparator 3315, depending on whether the engine speed is higher orlower than a predetermined level. This operation is identical to that inthe second embodiment and therefore will not be described again. Themonostable multivibrator 3301, on the other hand, applies a set signalto the set (S) of the reset-set flip-flop in response to a knockingpulse. In response to the set signal, the R-S flip-flop is raised tohigh state and held at high stage until a reset signal is appliedthereto from the counter 3318 or 3319. The R-S flip-flop is thusmaintained at high state for the period corresponding to a predeterminednumber of cycles set according to the engine speed from the occurrenceof a knocking. The output terminal of this R-S flip-flop (Q terminal) isconnected to the switch 3308 mentioned in the first and secondembodiments. The subsequent operation is identical to that of the firstembodiment and will not be explained again.

The predetermined time or predetermined cycles may be set in accordancewith the engine intake pressure or a combination of engine conditionsinstead of in accordance with the engine speed as in the first to thirdembodiments. Also, the electrical circuits making up the retard amountchanging circuit 33, the retard amount computing circuit 34 and theignition timing computing circuit 35 in the first to third embodimentsmay be replaced in whole or in part with equal effect by softwaretechniques by use of a microcomputer. Such replacements are included ina fourth embodiment shown in FIG. 10.

In FIG. 10, numeral 5 designates a 4-cylinder 4-cycle engine, numeral 1a knocking detector securely mounted on the engine 5 for detectingengine vibrations specific to the knocking, numeral 51 a starter, andnumeral 511 a starter switch. Numeral 6 designates a rotational anglesensor for measuring the rotational angle of the engine 5, whichproduces a top dead center signal when the engine 5 rotates to the topdead center and a rotational angle signal for each predetermined crankangle (such as 30 degrees in this embodiment) from the top dead center,the crank angle being obtained by dividing one engine revolution intoequal parts. Numeral 7 designates an intake pressure sensor formeasuring the intake manifold pressure transmitted from the intakemanifold 53 to the pipe 531. Numeral 52 designates a well-known fuelsupply device. Numerals 4 and 8 designate an ignitor and an ignitioncoil as an ignition actuator. The ignition timing control circuit 3determines the engine speed from the time intervals of the rotationalangle pulses produced from the rotational angle sensor 6 on the one handand computes the intake manifold pressure from the output voltage of thepressure sensor 7 on the other hand thereby to determine the engineoperating conditions. The circuit 3 also controls the ignition timing bydetecting the occurrence of a knocking from the output signal of theknocking detector 1. At the time of engine start when the ignitiontiming is controlled to a predetermined level, the voltage supplied fromthe starter switch 511 to the starter 51 is applied as a starter signalto the ignition timing control circuit 3. Also, since the energizationtime of the ignition coil is changed with the battery voltage, thebattery voltage is applied as a battery voltage signal to the ignitiontiming control circuit 3. Numeral 55 designates a power supply forgenerating the power of a voltage required by the ignition timingcontrol circuit 3 from the voltage of the battery 59 mounted on thevehicle.

The configuration of the ignition timing control circuit 3 included inthe system of FIG. 10 is shown in FIG. 11. Numeral 360 designates acentral processing unit for computing the ignition timing and includes amicrocomputer of 8 bits. Numeral 367 designates a read-only memory whichstores control programs and control constants. Numeral 368 designates arandom-access memory used for storing the control data during theoperation of the CPU 360 according to a control program. Numeral 361designates an interruption control section for effecting an interruptionin response to the generation of the rotational angle signal pulse fromthe engine rotational angle sensor 6.

A timer section 362 includes a 16-bit counter for counting the clockpulses generated for every 8 μs and a latch for holding the count eachtime of generation of the rotational angle signal from the rotationalangle sensor 6. By the interruption in response to the generation of arotational angle pulse, the CPU 360 reads out the value of the crankangle counter 363 to determine the engine rotational angle position onthe one hand and reads out the value of the latch of the timer section362 on the other hand. This operation is performed for two rotationalangle positions to determine the difference between two values of thelatch, thereby measuring the time required by the engine to rotatebetween the two rotational angles on the one hand and the engine speedon the other hand.

The crank angle counter section 363 counts up in response to therotational angle signal produced from the rotational angle sensor 6 andis reset to "0" when a rotational angle signal is generated followingthe top dead center signal into synchronism with engine rotations. It isthus possible to determine the engine rotational angle position by theunits of 30 degrees crank angle from the successive values of the crankangle counter produced by the CPU.

A digital input-output port 365 is used for input and output of logicsignals and is supplied with the voltage level supplied from the starterswitch 511 to the starter 51 to recognize that the starter switch 511 isturned on at the time of engine start. The port 365 is also used forgenerating a program interruption signal supplied to the interruptioncontrol section 361. The knocking detector circuit 31 is the same as theone included in the first embodiment and an output signal thereof in theform of a knocking pulse is applied to the digital input port 365.

The analog input port 364, which is for measuring the voltage of theanalog signal, subjects the battery voltage to analog-digital conversionin order to compensate for the output voltage signal of the intakepressure sensor 7 for measuring the intake manifold pressure of theengine 5 and the battery voltage for the energization time of theignition coil 8.

An energization-ignition control section 366 is for producingenergization and ignition signals for the coil current actuator circuitof the ignitor 4. This energization-ignition control section 366includes several down counters and, in response to the instructions ofthe CPU on the value of the crank angle counter for starting thecounting of the down counters and the down counts, is reduced to "0" forenergization and "1" for ignition when the value of the down counters is"0". Numeral 369 designates a common bus, through which control and datasignals are transmitted by the CPU for transmission and receipt of thecontrol and data of the peripheral circuits.

A method of computing the ignition timing will be explained. FIG. 12shows a flowchart of an example of the method of computing the ignitiontiming. First, a basic ignition timing θ_(B) (a two-dimensional mapincluding the engine speed and intake pressure) is determined, whichcorresponds to the operating conditions stored in the memory on thebasis of the engine speed Ne and the intake pressure Pm determined bythe rotational angle sensor and the intake pressure sensor signals. Ifthe intake pressure Pm is smaller than P_(l) (say, -360 mmHg), it isdecided that a light load is involved in which a knocking nevers occurs.If the intake pressure Pm is larger than P_(l), on the other hand, it isdecided whether or not the combustion cycle involved is a knocking cycledepending on whether or not a knocking pulse is received from theknocking detector circuit. If a knocking cycle is decided, the advancetimer is reset (A =0). The value of a cycle counter C for counting thecycles predetermined according to the engine conditions is read therebyto determine the number of ignition cycles between the present knockingand the preceding knocking. If the value of C is not zero, knockings areassumed to have occurred successively in the predetermined cycles andthe retard coefficient α is made α₂. If C is zero, on the other hand,the predetermined cycles or more have already passed, and therefore thecoefficient α is made α₁ (α₁ <α₂). In order to count the ignition cyclesfrom the present knocking, the cycle counter is set to a predeterminednumber of cycles corresponding to the engine speed and the intakepressure (C =Cij). Examples of the values Cij set by the cycle counterare shown in the table below. t,0270

The value of Cij is sej to zero for the engine speed of, say, more than4800 rpm in order to substantially nullify the function of changing theretard amount by the successive occurrence of knockings in that range.

The retard amount Δθ and the compensated ignition timing θc are computedfrom Δθ=60 ·Δθo and θc=θc+Δθ, where Δθo is the basic unit of retardamount and may take the value of 0.5° CA, for instance. Assuming that α₁=1 and α₂ =4, θΔ=2 CA (4 ×0.5) if knockings occur successively duringthe predetermined cycles, and Δθ=0.5 CA (1 × 0.5) otherwise. Thecompensated ignition timing θc is the retard from the basic ignitiontiming. The value θc has an upper limit θcmax which functions as alimiter for preventing a further retard. The final ignition timing θ forthe next ignition is determined from θ=θ_(B) -θ_(C).

In the case where the present combustion cycle is not a knocking cycle,on the other hand, the advance timer is counted up by one (A=A+1). Thecycle counter C is then counted down to count the number of ignitioncycles form the preceding knocking. Further, it is determined whether ornot the advance timer has reached a predetermined number, and if it hasreached the predetermined number, the compensated ignition timing isreduced by θ_(A) (such as 0.5° CA) thereby to correct the ignitiontiming in the advancing direction.

When Pm is smaller then P₁, a light load is involved under whichknockings do not occur, and therefore the advance timer A and the cyclecounter C are reset to zero while at the same time setting thecompensated ignition timing to zero. In this case, the ignition timing θis equal to θ_(B) for the most advanced condition. By rapidly attainingthe most advanced state under a light load, the performance loss whichotherwise might be caused by the retard is prevented. In this way, theignition timing is computed and the engine is ignited through theignitor and the coil.

It will be understood from the foregoing detailed description thataccording to the present invention, a successive occurrence of knockingsis detected to change the retard amount per knocking, and the periodduring which the successive occurrence of knockings occur is changedaccording to the engine conditions, thus leading to the great advantagethat the operating performances under both the normal and transientconditions are greatly improved. Further, according to the presentinvention, the retard amount per knocking is changed according to themanner of successive occurrence of knockings on the one hand and thefunction of changing the retard amount is substantially nullified underpredetermined engine conditions, with the result that the operatingperformances under both normal and transient conditions are improvedwhile at the same time reducing the erroneous decision on knocking andoutput decrease under predetermined operating conditions.

We claim:
 1. An ignition timing control system for internal combustionengines, comprising:an engine sensor for detecting conditions of theengine, a knocking detector circuit for detecting knockings of aninternal combustion engine, and producing an ignition timing retardamount per knocking, a control unit for generating an ignition timingcontrol signal in response to output signals of the engine sensor andsaid knocking detector, and an ignitor for generating an ignition signalin response to the ignition timing control signal from said controlunit, said control unit comprising: means for changing the retard amountper knocking depending on whether another knocking is decided before thelapse of a predetermined interval from the decision of a knocking, andmeans for changing said predetermined interval in accordance with theengine conditions detected by said engine sensor.
 2. An ignition timingcontrol system for internal combustion engines comprising:a knockingdetector circuit for detecting knockings of an internal combustionengine, and producing an ignition timing retard amount per knocking, acontrol unit for generating an ignition timing control signal inaccordance with an output signal produced from said knocking detector,an ignitor for generating an ignition signal in response to the ignitiontiming control signal from said control unit; said control unitcomprising: means for changing the retard amount per knocking dependingon whether another knocking is decided before the lapse of apredetermined interval from the decision of the knocking, knockingdetection means responsive to the output signal of said knockingdetector for comparing the output signal of said knocking detector witha reference value, and retard amount computing means responsive to aretard amount signal corresponding to a retard amount per one knockingderived from the output of said changing means; said knocking detectionmeans comprising a rectifier for rectifying the output signal of saidknocking detector, an integrator for integrating the output signal ofsaid rectifier to provide an average value of output signal of saidknocking detector, an offset voltage generator for providing a noisemargin signal to an output signal of said integrator, an adder forreceiving the output signal of said integrator and the output signal ofsaid offset voltage generator to provide a knocking decision level, anda comparator for comparing the output signal of said rectifier and theknocking decision level of said comparator to provide a knocking presentsignal.
 3. An ignition timing control system for internal combustionengines comprising:a knocking detector circuit for detecting knockingsof an internal combustion engine, and producing an ignition timingretard amount per knocking, a control unit for generating an ignitiontiming control signal in accordance with an output signal produced fromsaid knocking detector, an ignitor for generating an ignition signal inresponse to the ignition timing control signal from said control unit;said control unit comprising means for changing the retard amount perone knocking depending on whether another knocking is decided before thelapse of a predetermined interval from the decision of the knocking,said changing means comprising a monostable circuit responsive to theknocking present signal to provide a predetermined time signal, a firstelectrical switch responsive to the predetermined time signal to providea charging current signal and a discharging current signal, a capacitorcharged and discharged by the charging current signal and thedischarging current signal, a comparator for comparing the outputvoltage of said capacitor with a pickup signal of a signal generator toprovide an actuation signal, and a second electrical switch operable bythe actuation signal of said comparator to provide a first and a secondconstant current signal.
 4. An ignition timing control system forinternal combustion engines comprising:a knocking detector circuit fordetecting knockings of an internal combustion engine, and producing anignition timing retard amount per knocking, a control unit forgenerating an ignition timing control signal in accordance with anoutput signal produced from said knocking detector, an ignitor forgenerating an ignition signal in response to the ignition timing controlsignal from said control unit, wherein said control unit comprises:means for changing the retard amount per knocking depending on whetheranother knocking is decided before the lapse of a predetermined intervalfrom the decision of the knocking; knocking detection means responsiveto the output signal of said knocking detector for comparing the outputsignal of said knocking detector with a reference value; and retardamount computing means responsive to a retard amount signalcorresponding to a retard amount per knocking derived from the output ofsaid changing means, said retard amount computing means comprising anelectric switch operable by the knocking present signal of said knockingdetection means, a capacitor charge by said first and second currentsignals, and a current source connected in parallel with said capacitor.5. An ignition timing control system for internal combustion engines,including an engine sensor for detecting conditions of the engine, aknocking detector for detecting knockings of an internal combustionengine, a control unit for generating an ignition timing control signalin response to an output signal of the engine sensor and an outputsignal of said knocking detector, and an ignitor for generating anignition signal in response to the ignition timing control signalproduced from said control unit; wherein said ignition timing controlcircuit comprises means for changing the retard amount per knockingdepending on whether another knocking is decided before the lapse of apredetermined time interval from the decision of a knocking, means forchanging said predetermined interval in accordance with the engineconditions detected by said engine sensor, and means for substantiallynullifying the function of changing the retard amount underpredetermined engine conditions.
 6. A system according to claim 1wherein said control unit further comprises knocking detection meansresponsive to the output signal of said knock detector for comparing theoutput signal of said knock detector with a reference value, and retardamount computing means responsive to a retard amount signalcorresponding to a retard amount per one knocking derived from theoutput of said changing means.
 7. A system according to claim 6 whereinsaid knocking detection means comprises a rectifier for rectifiering theoutput signal of said knocking detector, an integrator for integratingthe output signal of said rectifier to provide an average value ofoutput siganl of said knocking detector, an offset voltage generator forproviding a noise margin signal to an output signal of said integrator,an adder for receiving the output signal of said integrator and theoutput signal of said offset voltage generator to provide a knockingdecision level, and a comparator for comparing the output signal of saidrectifier and the knocking decision level of said comparator to providea knocking present signal.
 8. system according to claim 1 wherein saidchanging means comprises a monostable circuit responsive to the knockingpresent signal to provide a predetermined time signal, a firstelectrical switch responsive to the predetermined time signal to providea charging current signal and a discharging current signal, a capacitorcharged and discharged by the charging current signal and thedischarging current signal, a comparator for comparing the outputvoltage of said capacitor with a pickup signal of a signal generator toprovide an actuation signal, a second electrical switch operable by theactuation signal of said comparator to provide a first and a secondconstant current signal.
 9. A system according to claim 8 wherein saidretard amount computing means comprises an electric switch operable bythe knocking present signal of said knocking detection means, acapacitor charged by said first and second current signal and a currentsource connected in parallel with said capacitor.
 10. A system accordingto claim 1 wherein said control unit includes a microcomputer comprisingthe steps of:deciding whether the occurrence of knocking is present orabsent; deciding through a value of a counter C whether thepredetermined interval beginning from the time when the occurrence of aprevious knocking is decided is lapsed or not; setting a retardcoefficient α to a first predetermined value α₁ when it is decided thatsaid predetermined time interval is lapsed; setting the retardcoefficient α to a second predetermined value α₂ when it is decided thatsaid predetermined time internal is not lapsed; setting the value ofcounter C to a third predetermined value; and computing a retard amountΔθ from the retard coefficient α.
 11. A system according to claim 1wherein said changing means provides a large retard amount when saidpredetermined interval is short and provides a small retard amount whensaid predetermined interval is long.